This invention relates to apparatus for recovering a frequency-converted chrominance component that is substantially free of cross-talk components and, more particularly, to such apparatus which is useful in recovering such frequency-converted chrominance components from a video signal recorder, such as a video tape recorder (VTR) of the type in which composite video signals are recorded with frequency-modulated luminance components and frequency-converted chrominance components, the latter being recorded in adjacent tracks and exhibiting a frequency interleaved relationship with respect to each other.
High density VTR's are known, such as described in U.S. Pat. Nos. 4,007,482 and 4,007,484, wherein a composite video signal is separated into its luminance and chrominance components, the luminance component being frequency-modulated to a higher frequency range and the chrominance component being frequency-converted to a lower frequency range. The frequency-modulated luminance component and the frequency-converted chrominance component then are superimposed, or combined, and recorded in successive, adjacent tracks. To obtain a high density of recording, such tracks are recorded without guard bands therebetween. To avoid undesired cross talk which may be picked up from an adjacent track when a particular track is scanned, these patents describe techniques by which the luminance and chrominance components are recorded. The well-known phenomenon known as azimuth loss is used to record successive tracks with different recording transducers, or heads, these heads having gaps with different azimuth angles. Thus, when a relatively higher frequency signal, such as the frequency-modulated luminance component, that is recorded by, for example, head A is reproduced by head B, substantial attenuation of that frequency-modulated luminance component will obtain, thereby minimizing or avoiding cross talk interference therewith. Of course, such azimuth loss is not present when the same head (for example, head A) is used for reproduction as was used for recording.
Although this phenomenon of azimuth loss is turned to account to avoid cross talk interference in the reproduction of the frequency-modulated luminance components, significant attenuation is not present when different heads are used to reproduce the relatively lower frequency signals, such as the frequency-converted chrominance components. The aforementioned patents describe particular techniques which are used to record and reproduce and chrominance components so as to minimize, or avoid, cross talk interference. More particularly, the frequency of the chrominance subcarrier is modified such that the chrominance subcarrier frequency that is recorded in one track differs from the chrominance subcarrier frequency that is recorded in the next adjacent track. In particular, these different chrominance subcarrier frequencies exhibit a so-called "frequency interleaved" relationship with respect to each other. That is, the chrominance subcarrier frequency, and various harmonics thereof, recorded in one track differs from the chrominance subcarrier frequency, and corresponding harmonics thereof, recorded in the next adjacent track such that, if these frequencies are superimposed one upon the other, they would appear to be interleaved. This interleaved relationship is particularly advantageous in eliminating cross-talk interference. When the reproduced chrominance component is passed through a comb filter, if the frequencies at which that filter exhibits maximum attenuation correspond to the various cross talk frequencies picked up from the adjacent track, then cross talk interference in the chrominance component is substantially attenuated and, thus, eliminated.
In the aforementioned patents, the frequency interleaved relationship between the chrominance components which are recorded in adjacent tracks is attained by, for example, inverting the phase of the chrominance subcarrier at each successive line interval in one track, and maintaining the phase of the chrominance subcarrier constant from one line interval to the next in the next adjacent track. This technique is advantageous because the chrominance subcarrier frequency may be the same in each track; but the aforementioned phase modulation is tantamount to recording the chrominance component with different subcarrier frequencies.
In VTR's wherein the composite video signals are recorded in the aforedescribed manner, that is, the composite video signals are recorded by frequency-modulating the luminance component to a higher frequency range while frequency-converting the chrominance component to a lower frequency range, making sure that the frequency-converted chrominance subcarrier in adjacent tracks exhibits the aforementioned frequency interleaved relationship, the composite video signal which is recorded on one record medium, that is, magnetic tape, may be transferred to a second record medium, or magnetic tape. Such editing, or dubbing, operations heretofore have been carried out by recovering the frequency-modulated luminance component and the frequency-converted chrominance component, operating separately on such components to return them to their original frequency ranges, re-forming the original composite video signal, and then separating that re-formed composite video signal into its separate luminance and chrominance components, whereupon these separate components are processed in the aforedescribed manner. Such processing of at least the chrominance component may introduce undesired deteriorations into the signal, thus resulting in corresponding deteriorations or degradation of the quality of the picture which ultimately is reproduced therefrom.
To avoid the foregoing disadvantage, it may be thought that the frequency-converted chrominance component, as reproduced from the first record medium, may be supplied directly for recording on the second record medium while remaining in its frequency-converted condition. This would avoid frequency re-conversion back to its original frequency range and then, once again, frequency-converting the chrominance component to its lower frequency range. However, when the composite video signals are recorded in adjacent tracks without guard band, the reproduced frequency-converted chrominance component often is accompanied by undesired cross talk interference. Such cross talk must be eliminated from the frequency-converted chrominance component before it can be re-recorded. However, in cross talk elimination techniques which have been employed heretofore, cross talk interference is removed from the reproduced chrominance component only after that component has been frequency re-converted back to its original frequency range. Thus, it has not been possible to transfer a frequency-converted chrominance component, substantially free of cross talk components, without first re-converting the chrominance component back to its original frequency range. However, such re-conversion, followed by a subsequent frequency conversion, is not desired.